Color Properties in Domain Components

• Mar 12, 2021
• 3 minutes to read

This topic demonstrates two approaches to store a System.Drawing.Color property value in the database using the Domain Components technology.

1. The first approach is to implement a Value Converter.

   C#

   using System;
   using System.Drawing;
   using DevExpress.Xpo.Metadata;
   // ...
   public class ColorValueConverter : ValueConverter {
       public override Type StorageType {
           get { return typeof(Int32); }
       }
       public override object ConvertToStorageType(object value) {
           if(!(value is Color)) return null;
           Color color = (Color)value;
           return color.IsEmpty ? -1 : color.ToArgb();
       }
       public override object ConvertFromStorageType(object value) {
           if(!(value is Int32)) return null;
           Int32 argbCode = Convert.ToInt32(value);
           return argbCode == -1 ? Color.Empty : Color.FromArgb(argbCode);
       }
   }
   

   VB.NET

   Imports System
   Imports System.Drawing
   Imports DevExpress.Xpo.Metadata
   ' ...
   Public Class ColorValueConverter
       Inherits ValueConverter
       Public Overrides ReadOnly Property StorageType() As Type
           Get
               Return GetType(Int32)
           End Get
       End Property
       Public Overrides Function ConvertToStorageType(ByVal value As Object) As Object
           If Not(TypeOf value Is Color) Then
               Return Nothing
           End If
           Dim color As Color = CType(value, Color)
           Return If(color.IsEmpty, -1, color.ToArgb())
       End Function
       Public Overrides Function ConvertFromStorageType(ByVal value As Object) As Object
           If Not(TypeOf value Is Int32) Then
               Return Nothing
           End If
           Dim argbCode As Int32 = Convert.ToInt32(value)
           Return If(argbCode = -1, Color.Empty, Color.FromArgb(argbCode))
       End Function
   End Class
   

   After that, decorate properties that are need to be converted with the ValueConverterAttribute and the converter will be called on each attempt to store or acquire a value of the System.Drawing.Color type.

   C#

   using DevExpress.ExpressApp.DC;
   using DevExpress.Persistent.Base;
   using DevExpress.Xpo;
   using System.Drawing;
   //...
   [DomainComponent, NavigationItem]
   public interface IMyColor {
       [ValueConverter(typeof(ColorValueConverter))]
       Color Color { get; set; }
   }
   

   VB.NET

   Imports DevExpress.ExpressApp.DC
   Imports DevExpress.Persistent.Base
   Imports DevExpress.Xpo
   Imports System.Drawing
   '...
   <DomainComponent, NavigationItem> _
   Public Interface IMyColor
       <ValueConverter(GetType(ColorValueConverter))> _
       Property Color() As Color
   End Interface
   

2. Another approach is to convert the System.Drawing.Color type to System.Int32 on property implementation using Get_PropertyName and Set_PropertyName methods of the Domain Logic class, as shown below.

   C#

   using DevExpress.ExpressApp.DC;
   using DevExpress.Persistent.Base;
   using System.ComponentModel;
   using System.Drawing;
   //...
   [DomainComponent, NavigationItem]
   public interface IMyColor {
       [Browsable(false)]
       int PersistentColor { get; set; }
       [NonPersistentDc]
       Color Color { get; set; }
   }
   
   [DomainLogic(typeof(IMyColor))]
   public class MyColorLogic {
       public static Color Get_Color(IMyColor MyColor) {
           return Color.FromArgb(MyColor.PersistentColor);
       }
       public static void Set_Color(IMyColor MyColor, Color value) {
           MyColor.PersistentColor = value.ToArgb();
       }
   }
   

   VB.NET

   Imports DevExpress.ExpressApp.DC
   Imports DevExpress.Persistent.Base
   Imports System.ComponentModel
   Imports System.Drawing
   '...
   <DomainComponent, NavigationItem> _
   Public Interface IMyColor
       <Browsable(False)> _
       Property PersistentColor() As Integer
       <NonPersistentDc> _
       Property Color() As Color
   End Interface
   
   <DomainLogic(GetType(IMyColor))> _
   Public Class MyColorLogic
       Public Shared Function Get_Color(ByVal MyColor As IMyColor) As Color
           Return Color.FromArgb(MyColor.PersistentColor)
       End Function
       Public Shared Sub Set_Color(ByVal MyColor As IMyColor, ByVal value As Color)
           MyColor.PersistentColor = value.ToArgb()
       End Sub
   End Class
   

   Note

   If the type’s class does not have an appropriate conversion method (Color.ToArgb in this case), implement a Type Converter and use it any time you need a value conversion between the type you need to store and an ORM-friendly type.